Abstract

Three air-sprung heavy vehicles (HVs) were instrumented and tested on typical suburban and highway road sections at representative operational speeds. The vehicles used were a tri-axle semi-trailer towed with a prime mover, an interstate coach with 3 axles and a school bus with 2 axles. Dynamic wheel force data were gathered for the purposes of: informing the QUT/Main Roads project Heavy vehicle suspensions - testing and analysis; and  providing a reference source for future projects. This report sets down the methodology for, and dynamic wheel force results of, the testing. Accordingly, time-series plots are provided to show indicative peak and dynamic wheel forces during typical use. Frequency-series analysis was performed on the wheel force data. The results are documented in the Appendices. Summaries of the wheel forces' peak values, means and standard deviations are provided in tables in the body of the report. Over the past 10 years the Australian road transport network has been opened up to increasing numbers of HML vehicles and lengths of road declared to be HML routes. With this increase, there has been a concomitant number of HVs fitted with RFS. Accordingly, the HV fleet has become more homogenous than in the past. This then provides for a continuing homogenisation of the HV fleet with convergent suspension characteristics, particularly with respect to body-bounce frequencies, namely:  increasing homogeneity of the parameters of the RFS-equipped HV fleet will result in more highly correlated wheel-forces. For a heavy vehicle fleet with increasingly homogenous suspension characteristics, pavement distress will likely be concentrated in patches distributed longitudinally; and  this concentration will predominate at intervals of approximately 14 - 20 m for highway segments, particularly those with laden semi-trailer traffic. That spatial repetition would need to be addressed eventually had been foreseen (LeBlanc, 1995); suspensions with common parameters will bounce their wheels onto the same places on the pavement after encountering a bump. The results from this report suggest that is the case. With the homogeneity of the HV fleet now upon us, the need for research into the effects of mandated uniform HV suspension characteristics is more urgent than when first mooted by researchers such as LeBlanc (1995) almost 15 years ago. Dynamic pavement forces created by heavy vehicles have been modelled for some decades. The current pavement models do not always account for dynamic peak forces, however. More research needs to be done on the models used to design pavements, in particular the dynamic aspects of heavy vehicle loadings. This report should contribute to that process by providing a set of input parameters for pavement researchers to use for further development of their current models.

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